1. Field of the Invention
The present invention relates to a developing roller, a developing device, a process cartridge, and an image forming apparatus.
2. Description of the Related Art
One-component development is known as a small-sized, inexpensive developing system. In this one-component development, however, it is necessary to apply high linear pressure to toner particles using a regulating blade for stabilizing charging conveyance. As a result, a surface of a developing roller suffers filming of toner particles, which problematically shortens the service life of the developing roller. In order to solve this problem, there has been proposed a technique of preventing filming by improving releasability of a surface layer of the developing roller.
For example, for the purpose of providing an electroconductive roller which can provide a clear image even under severe printing conditions in a HH environment and which is especially effective to prevention of fogging on a white background, an invention of an electroconductive roller has been disclosed, which includes an elastic layer and at least one layer thereon, wherein the outermost layer is a layer where a fluorine-containing urethane resin has been added to an acrylic resin serving as a binder resin component (see Japanese Patent Application Laid-Open (JP-A) No. 2011-215467).
Such an improvement in releasability can prevent filming, but its improvement mechanism is due to localization of fluorine near the surface. Thus, an increased amount of fluorine near the surface relatively reduces charging sites near the surface. As a result, there has been a problem that even a small extent of filming tends to reduce charging.